1831.] Forms of Vibrating Fluids. 335 



(29. 31), when the membrane was covered by a plate of glass, 

 is a necessary consequence of the arrangements there made, 

 and tends to show how influential the action of the air or other 

 including medium is in all the phenomena considered in this 

 paper. No incompatible principles are assumed in the expli- 

 cation given of the arrangement of the forces producing the 

 two classes of effects in question ; and though by variation of 

 the force of vibration and other circumstances, the one effect 

 can be made, within certain limits, to pass into the other, no 

 anomaly or contradiction is thus involved, nor any result pro- 

 duced, which, as it appears to me, cannot be immediately ac- 

 counted for by reference to the principles laid down. 

 Royal Institution, March 21, 1831. 



APPENDIX. 



On the Forms and States assumed by Fluids in contact with 

 vibrating Elastic Surfaces. 



63. When the upper surface of a plate vibrating so as to 

 produce sound (2. 6) is covered with a layer of water, the water 

 usually presents a beautifully crispated appearance in the neigh- 

 bourhood of the centres of vibration. This appearance has 

 been observed by Oersted*, Wheatstonef, Weber J, and pro- 

 bably others. It, like the former phenomena which I have en- 

 deavoured to explain, has led to false theory, and being either 

 not understood or misunderstood, has proved an obstacle to 

 the progress of acoustical philosophy. 



64. On completing the preceding investigation, I was led to 

 believe that the principles assumed would, in conjunction with 

 the cohesion of fluids, account for these phenomena. Experi- 

 mental investigation fully confirmed this expectation, but the 

 results were obtained at too late a period to be presented to 

 the Royal Society before the close of the Session ; and it is 

 only because the philosophy and the subject itself is a part of 

 that received into the Philosophical Transactions in the pre- 

 ceding paper, that I am allowed, by the President and Council, 

 the privilege of attaching the present paper in the form of an 

 Appendix. 



* Lieber's Hist, of Natural Phenomena for 1813. 



t Annals of Philosophy, N. S. vi. p. 82. J Wellenlehre, p. 4 14. 



